The invention relates to a device for monitoring a friction clutch, particularly an automatized friction clutch of a motor vehicle.
From DE-A-36 01 708 it is known, for monitoring the friction clutch of a motor vehicle, to measure the torque produced by the engine of the motor vehicle, or possibly to determine it through a stored family of characteristics of the engine and, by means of a computer device, to compute friction performance data by multiplying the torque by the difference rotational speed between input rotational speed and output rotational speed of the clutch. The computer device adds up friction performance values detected in succession and compares this friction work mean value thus formed with a limit value. When the limit value is exceeded a warning signal is switched on which indicates the thermal overload. The known monitoring device, however, operates relatively inaccurately as it is unable to distinguish between momentary peak loading and the clutch continuous loading.
From DE-A-38 28 128 a device is known for monitoring an automatized friction clutch of a motor vehicle, in which again a computer device calculates data dependent upon the instantaneous torque and the instantaneous difference between input rotational speed and output rotational speed of the clutch, which represent the instantaneous frictional performance of the clutch. By means of the summation of the friction performance data over several time intervals of different duration a differentiation is made between a short-term, medium-term and a long-term temperature behaviour of the clutch. Associated with the frictional operation means values detected for the individual time intervals are again limit values on the exceeding of which either warning signals are emitted, or the control characteristic at which a control automatically engages or releases the clutch, is governed. In order to simulate the short-term, medium-term and long-term cooling behaviour of the clutch, correction values are periodically extracted from the friction work means values.
This known device also permits only a relatively inaccurate monitoring. On the one hand, errors are added up when calculating the friction performance data when these are summed up for arriving at the friction work mean values. The clutch continuous loading can therefore be monitored only very inexactly. In addition, with the known device the cooling behaviour of the clutch is considered only very roughly, as the cooling behaviour depends upon a plurality of parameters not taken into consideration, such as, e.g., the outside air temperature, driving speed and the rotational speed of the clutch. Accordingly, a monitoring of the clutch continuous loading is therefore possible only limitedly. The same applies also to the monitoring of the peak loading as the loading bearable is dependent upon the output temperature of the clutch.
An inexact determination of the friction work mean values results in the premature inception of the overload protective measures in a cold clutch resulting in an unnecessary loss of comfort, while, when the clutch has been highly loaded for a lengthy period, peak loadings can ruin the clutch before the overload protection is enabled.